Some hatchlings can take well over 48 hours from their initial slit to absorb all the yolk before fully emerging from the egg. But if you haven't seen at least the hatchling's nose poking out for 8 hours, I would recommend that you open the egg up to see what's going on.
I've had the odd hatchling make such a small slit that they literally cannot get their body out of it, only their head. After losing one like that, I now always use my 2 pairs of surgical forceps (but tweezers will do) to gently gran the edges of the slits and pull/tear the opening larger. I do this on each and every egg.